1. Field of the Invention:
The present invention relates to a wiper driving apparatus, and more particularly to a wiper driving apparatus mounted on vehicles such as automobiles and the like used, for example, in the snow country.
2. Related Art Statement:
In general, in a wiper driving apparatus mounted on a vehicle such as automobiles and the like, in order to ensure a safe operation of the vehicle, there is provided an automatic wiper home position stop device which enables a wiper blade of the vehicle to return to its home position and stop thereat even when the user turns off a wiper switch of the vehicle at any time.
In a conventional wiper home position stop device of this type: an electrically-conductive plate, which is partially provided with an electrically non-conductive part, is fixed to an axial-end surface of a driving gear; electrical-contact points which constitute, together with the electrically-conductive plate, a switch for opening and closing an electric circuit of an electric motor is so disposed in a housing as to be slidably moved along the electrically-conductive plate when the driving gear is rotatably driven; and, even when the user turns off the wiper switch of the vehicle at any time, both the electrically-conductive plate and the electrical-contact points form an electric circuit for enabling the wiper blade of the vehicle to return to its home position in which, when the wiper blade is at its home position, the electrical-contact point is brought into a contact with an electrically non-conductive part of the electrically-conductive plate to break an electric circuit of a wiper motor, and then, the circuit is shortened to make an electric brake act, whereby operation of the wiper motor is automatically stopped.
However, in a vehicle provided with a conventional wiper driving apparatus having such wiper home position stop device, a bank of snow deposited over a lower part of the windshield of the vehicle often prevents the wiper blade from returning to its home position. Under such circumstances, the driving gear of the wiper driving apparatus is subjected to an external force which acts on the driving gear in a direction counter to its normal rotational direction or driving direction to cause the electrically-conductive plate and the electrical-contact point to alternately make and brake the circuit of the wiper motor, thus generating a chattering phenomenon. When the chattering occurs, the wiper driving apparatus is heated to a considerably high temperature, and is thereby damaged in quality and durability. This is a problem inherent in the conventional wiper driving apparatus.